"It’s really helpful to get to know your own cycle," she said. "If you have your period every 28 days you can predict exactly when you're ovulating."

LISTEN: This woman has an IUD. And she wants to tell us all about it. (Post continues below.)

"But if you’re someone with really erratic bleeding, you can’t really know if your bleeding is due to an egg not being fertilized or something else," Dr. Dweck instructed. "It might be unsafe to have sex during that time."

This post originally appeared on Mamamia, Spring.St's Australian sister site. You can read it here.